[BUG?] Array#slice!() adds elements to Array

Moin.

The following behavior is undocumented and IMHO counter-intuitive and of 
little use:

# Limit an array to three elements
irb(main):001:0> obj = [1]; obj.slice!(3 .. -1); obj
=> [1, nil, nil]

I've always thought about .slice!() as a good way of truncating. The 
above conflicts with that use of the method.

Note that I am okay with having that behavior for obj[3 .. -1] = [] so 
it would still be reachable in case anybody finds it useful. If that is 
too long I think it would also be okay to add Array#size= for that case.

If you think that the above makes sense the documentation should still 
be updated to point out that case and I think it would be a good idea to 
add a method for truncating arrays in that case.

Kind regards,
Florian Gross